The present invention relates generally to apparatus and methods for conveying particulate solid material in large scale industrial processes.
The present invention has particular application to large scale industrial processes for the treatment of coal, oil shale or the like where large amounts of solid material must be conveyed and metered to different processing apparatus and areas within a particular processing plant.
Presently, screw feeders are typically utilized throughout large scale industrial operations for transporting and metering solid materials. For example, in the processing of oil shale and coal, screw feeders are often specified as the means for introducing the raw carbonaceous material into processing apparatus. Although conventional screw feeders are widely used in industry, they are notorious for problems resulting from jamming due to material wedging between the outside of the screw flights and the trough or enclosure within which the screw rotates. As material begins to wedge and jam within the typical screw feeder, continued rotation of the screw increases pressure and compaction of the material at the stoppage site until a highly compacted plug is formed. The screw feeder continues to turn until the compressed plug or massive material becomes so large that the power or torque capabilities of the driving motor is exceeded. At this point, the only means by which the plug can be removed from the typical screw feeder is to disassemble and remove the screw from its enclosure.
In order to prevent severe jamming in screw type feeders, shear pins have been inserted in the screw feed drive system to prevent excessive loading and jamming of the screw feed conveyor. These pins are designed to shear prior to excessive screw loading to prevent severe compacting and plugging of the screw feeder trough or enclosure. In this way, clean-out of the screw feed conveyor is made easier since severe compaction and plugging of the conveyor tube is eliminated due to shearing of the pin prior to development of excessive torque loading on the screw. Even so, the screw feeders are still prone to jamming and must be cleaned out every time a shear pin is broken. In addition, shear pins which are continually stressed and strained during operation of the screw feed conveyor are subject to premature failure at loads normally encountered during conveyance of the solid materials.
The intermittent breakdown of screw feeders due to jamming and other system failures, is not only time-consuming but is quite costly due to the shutdown of an entire processing plant resulting from such a conveyance system failure. Accordingly, it is apparent that there is a present need for a non-jamming method and apparatus for conveying and metering solid materials.